Purification of butadiene



Jan. 2, 1945. w g SEMON ET AL 2,366,361

PURIFICATIGN 0F BUTADIENE Filed Sept. 30. 1939 Patented Jan. 2, 1945 PURIFICATION OF BUTADIENE Waldo L. Semen, Silver Lake, and David Craig, Cuyahoga Falls, Ohio, asslgnors to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application September 30, 1939, Serial No. 297,344

Claims.

This invention relates to separation or the components of substantially constant boiling mixtures and particularly to the separation of butadiene from butylene and butane.

It is known that butadiene can be enriched by distillation through a fractionating column down which flows a selective solvent for the butadiene. Processes of this kind which have been disclosed heretofore have all been continuous and have suffered from the inflexibility and necessity for meticulous control which characterize continuous dlstillations, but to a greatly enhanced degree, because the solvent introduces additional variables.

We have discovered that butadiene can readily be purified by selective extraction from vapors of crude butadiene, in a batch process, and that such a process avoids most of the difliculties encountered in continuous processes.

The continuous purification processesheretofore known resemble the batch process of this invention in some of the ways in which continuous fractional distillation resembles batch distillation, but in some respects exhibit fundamental diiierences.

We have discovered that significant enrichment of butadiene in admixture with butylene and butane cannot be accomplished unless ratio of rate of supply of solvent to rate of removal of impurities (butylene and butane) exceeds a critical value, analogous to the critical reflux ratio in ordinary fractionation. This ratio is a fairly large number (in the neighborhood of to 20 in the case of some of the more useful selective solvents), hence the volume ,of solvent which must be handled is many times the volume of butadiene recovered. This means that if an ordinary type of batch still is employed, the still kettle must be large enough to contain not only the original charge but also the total volume of solvent, hence the true capacity of the still is a very small fraction of the volumetric capacity of the kettle. We have accordingly devised a preferred method and apparatus in which this inconvenience is avoided.

In the accompanying drawing one embodicommunicates with a fractionating column 5 w callv. The crude liquid butadlene is charged through an inlet l in kettle 2 which is provided v with a temperature controlling means such as the Jacket 3. The vapor outlet 4 of the kettle communicates with a fractionating column 8 which is preferably a bubble cap plate column containing at least fifteen plates and desirably twenty to thirty plates, although other types of columns equivalent to such a plate column may be used. A solvent inlet 1 is provided at or near the top of the column. At the top of the column a conduit 8 carries elliuent vapors to a condenser 9, whence the condensed impurities are removed at Ill. Optionally the condensate may be divided and a portion returned as reflux through a liquid seal H to the uppermost plate or plates l2 to scrub traces of solvent from the eflluent vapors, but the reflux and the scrubbing plates can obviously be omitted if the solvent used is not appreciably volatile. The liquid reaching the bottom of the column passes through valve l3 and liquid seal it into a boiler I5 provided with heating means such as steam coil l6. One or more bubble cap plates ll may be provided between the liquid seal I4 and the boiler is so that the solution flowing into the boiler can scrub out any solvent contained in the vapors from the boiler. Additional plates l8 and a dephlegmator Ill may be provided above the point of entrance of the solution through liquid seal it, in order that refluxing condensate may scrub the last traces of solvent from the vapors. The dephlegmator I! and plates l8 may be omitted it the solvent is only slightly volatile, and if it is substantially non-volatile even the plate l1 may be omitted. The vapors from the boiler l5 pass back to the kettle 2 through valve 20 and conduit 2|, which preferably extends to the bottom of the kettle so that the vapors pass directly into the liquid therein. The bottom of the boiler I5 is connected through conduit 22, pump 23 and cooler 24 with a reservoir 25, whence the solvent is returned through valve 25 to the solvent inlet 7. A connection may also be provided for returning liquid from the bottom of the fractionating column 5 to the kettle 2 through a valve and auxiliary connection 21, which is normally kept closed.

In operation of the apparatus, the kettle 2 may be nearly filled with crude butadiene. A selective solvent for butadiene is started flowing down the column from reservoir 25 and is recirculated by pump 23, and the kettle is warmed by means of the jacket 3 to start distillation. The solvent, descending countercurrent to the ascending vapors, preferentially dissolves butadiene from the vapors, which progressively become leaner in this constituent as they approach the top of the column, whence they are finally removed. The butadiene is stripped from the solvent in the boilzer l5 and returned to the batch in the kettle To attain a satisfactory separation, the solvent should be one which has a satisfactory selectivity for the butadiene, and the ratio of rate of supply of solvent to rateoi removal of impurities should exceed the critical value heretofore mentioned. Suitable solvents are liquids which dissolve moderate proportions of butadiene at the temperature and pressure used, and which preferably contain multiple bonds between carbon atoms or between a carbon and another atom; including organic halogen compounds, alcohols, ethers, aldehydes, ketones, esters, amines, amides, nitriles, nitro compounds, and the like such as ethylene dichloride, chlorhydrin, dichlorether, methanol, butenol, acetaldehyde, crotonaldehyde, ethyl-hexenal, acetone, mesityl oxide, glycol diacetate, aniline, formarnide, acetonitrile, nitrobutane, nitrobenzene, etc. Hydrocarbons are not very selective although some unsaturated hydrocarbons such as styrene give fairly good results; Those materials which are not very good solvents for butadiene should be employed at low temperatures or at increased pressures in order to reduce the volume of solvent required to dissolve the butadiene, while materials which dissolve butadiene very readily should be employed at higher temperatures or lower pressures to reduce the solubility of the hydrocarbon vapors and thus maintain the maximum selectivity. For example, furfural which has only a limited solubility for butadiene gives best results at about 1 C. at atmospheric pressure, but mesityl oxide gives good separation at (3., whereas ethylene dichloride does not show satisfactory selectivity until its temperature is raised to about 30 C. These temperatures can readily be regulated through the cooler 24. The critical ratio of rate of supply of solvent to removal of impurities is about 12 for furfural at 1 C. and about 15 for mesityl oxide at 10 C., during the initial stages of the separation oi a mixture containing about 50% butadiene. At the end of the separation, when the butadiene concentration is higher, the critical ratio may increase somewhat, hence an operating ratio somewhat greater, say about 20, snould be selected, or the ratio may be increased as the separation progresses.

When circulation of the solvent and boiling of the crude butadiene are established, heat is supplied through the coil I. to boil dissolved butadiene out 01' the solvent. It is not necessary that the butadiene be completely eliminated, since the solvent is continuously recirculated, but it is desirable that as much as possible be boiled out, to prevent loss or some of th residual butadiene from the top of the column along with the vapors of the impurities. It is also not essential that the butadiene vapor be completely separated from solvent vapors in the boiler, so long as the volume of solvent accompanying the butadiene does not appreciably exceed the volume of impurities removed, but again a sharp separation is desirable because it reduces the labor of dually isolating the butadiene. The heat supplied through the coil is is therefore regulated to strip the solv nt as completely as possible without driving solvent vapors beyond the plates Hand It. The temperature of the contents or the kettle 2 is then regulated by circulation of fluid through the jacket I to maintain a rate or boiling which will cause impurities to issue at ill at the proper rate relative to the rate of solvent circulation.

In the preierred process, the vapors from the kettle, ascending the column, saturate the desoending solvent, and are progressively deprived of their butadiene content by continuous interchange with the saturated solution. At the top of the column the vapors consist almost entirely of impurities and are condensed, a portion being returned as reflux to the scrubbing plate I! to prevent solvent losses, and the remainder being withdrawn. The solvent at the bottom of the column is saturated with a mixture slightl richer in butadiene than the vapors issuing from the kettle. The solvent is stripped by boiling and is separated from the mixture under treatment by the plates II and II, the stripped solvent being cooled and recirculated. The vapors stripped from the solvent are reintroduced into the batch in the kettle and furnish part oi the heat for distilling the batch.

After most of the impurities have been eliminated it is advantageous to reduce the rate of distillation to obtain as sharp a separation as possible. When the butadiene content of the eillux begins to rise an intermediate fraction (which may be returned to the next batch) is taken, and when it approaches the desired conoentration, the operation is interrupted. The kettle 2 will then contain almost pure butadiene, which may be distilled if desired, either in the same or in other apparatus, to separate it from any traces of solvent which may have been carried into it. If the butadiene is to be distilled in the same apparatus it is only necessary to stop the flow of solvent by closing the valve 26, isolate the kettle and iractionating column from the stripping column by closing the valves l3 and 20, provide for the return of reflux to the kettle by opening valve 21, and continue the operation as an ordinary fractional distillation.

In actual practice a mixture of butane, butylene and butadiene containing about 60% butadiene is separated by means of an apparatus such as is described above, with 30 bubble cap plates in the separating column, using mesityl oxide at 10 C. as the solvent and a ratio of solvent flow to removal of impurities of about 20, into a mixture of impurities containing from 2 to 5% butadiene and amounting to about 30% of the mixture, an intermediate fraction (including the holdup on the plates) amounting to somewhat over 15% of the mixture, and a residue in the kettle of butadiene amounting to about 50% of the original mixture.

We claim:

1. A batch method of purifying butadiene mixed with other hydrocarbons of similar boiling point, which comprises distilling a batch of the mixed liquid hydrocarbons, missing the vapors through a fractionating column countercurrent to a liquid, relatively non-volatile, selective solvent ior butadiene at such a rate that the ratio 01 rate 0! pply 01 solvent to rate 01' withdrawal oi unwanted hydrocarbons from the head of the column exceeds the critical value, separating from the solvent which has passed down the column the hydrocarbons dissolved therein, and withdrawing the stripped solvent and returning the hydrocarbons separated from the solvent to the original batch, until the hydrocarbons other than :utagiene are substantially eliminated from the atc 2. A batch method of purifying butadiene mixed with other hydrocarbons of similar boiling point, which comprises distilling a batch of the mixed liquid hydrocarbons, passing the vapors through a tractionating column countercurrent to a liquid, relatively non-volatile, selective solvent for butadiene at such a rate that the ratio of rate of supply of solvent to rate of withdrawal oi. unwanted hydrocarbons from the head of the column exceeds the critical value, heating the solvent which has passed down the column to boil out the hydrocarbons dissolved therein, and withdrawing the stripped solvent and returning the hydrocarbons thus separated from the solvent to the original batch, until the hydrocarbons other than butadiene are substantially eliminated from the batch.

3. A batch method of purifying butadiene mixed with other hydrocarbons of similar boilin point, which comprises distilling a batch of'the mixed liquid hydrocarbons, passing the vapors through a fractionating column countercurrent to a liquid, relatively non-volatile, selective solvent for butadiene at such a rate that the ratio 01' rate of supply of solvent to rate of withdrawal of unwanted hydrocarbons from the head of the column exceeds the critical value, heating the solvent which has passed down the column to boil out the hydrocarbons dissolved therein, and withdrawing the stripped solvent and returning the hydrocarbon vapors thus separated from the solvent to the original batch under its liquid surface, until the hydrocarbons other than butadiene are substantially eliminated from the batch.

4. A batch method of purifying butadlene mixed with other hydrocarbons of similar boiling point, which comprises distilling a batch of the mixed liquid hydrocarbons, passing the vapors through a. fractionating column countercurrent to a liquid, relatively non-volatile, selective solvent tor butadiene at such a rate that the ratio of rate of supply of solvent to rate oi withdrawal of unwanted hydrocarbons from the head of the column exceeds the critical value, heating the solvent which has passed down the column to boil out the hydrocarbons dissolved therein, passing vapors boiled from the solvent in countercurrent contact with solution flowing from the column to deprive the vapors of their solvent content, and withdrawing the stripped solvent and returning the hydrocarbon vapors thus separated from the solvent to the original batch under its liquid surface, until the hydrocarbons other than butadiene are substantially eliminated from the batch.

5. The method of claim 4 in which the stripped solvent is cooled and recirculated through the column.

DAVID CRAIG. WALDO L. SEMON.

CERTIFICATE OF C ORREC'I'ION.

Patent No. 2,366,} 61.

January 2, 19145.

ALDO L. SEION; ET AL.

It is hereby certified that error appears in the printed specification of theebove numbered patent requiring correction as follows: Page 1, first column, lines 1 ,6 to 1+5 inclusive, for "drawing one e nbodicommunicates with a fractionating column 5 w cally" read --drawing one embodiment of the apparatus is shown diagrammatically; and that the saIdLetters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of May, A. D. 1915.

(Seal) Leslie Frazer Acting Commissioner of Patents.

rate of supply of solvent to rate of withdrawal oi. unwanted hydrocarbons from the head of the column exceeds the critical value, heating the solvent which has passed down the column to boil out the hydrocarbons dissolved therein, and withdrawing the stripped solvent and returning the hydrocarbons thus separated from the solvent to the original batch, until the hydrocarbons other than butadiene are substantially eliminated from the batch.

3. A batch method of purifying butadiene mixed with other hydrocarbons of similar boilin point, which comprises distilling a batch of'the mixed liquid hydrocarbons, passing the vapors through a fractionating column countercurrent to a liquid, relatively non-volatile, selective solvent for butadiene at such a rate that the ratio 01' rate of supply of solvent to rate of withdrawal of unwanted hydrocarbons from the head of the column exceeds the critical value, heating the solvent which has passed down the column to boil out the hydrocarbons dissolved therein, and withdrawing the stripped solvent and returning the hydrocarbon vapors thus separated from the solvent to the original batch under its liquid surface, until the hydrocarbons other than butadiene are substantially eliminated from the batch.

4. A batch method of purifying butadlene mixed with other hydrocarbons of similar boiling point, which comprises distilling a batch of the mixed liquid hydrocarbons, passing the vapors through a. fractionating column countercurrent to a liquid, relatively non-volatile, selective solvent tor butadiene at such a rate that the ratio of rate of supply of solvent to rate oi withdrawal of unwanted hydrocarbons from the head of the column exceeds the critical value, heating the solvent which has passed down the column to boil out the hydrocarbons dissolved therein, passing vapors boiled from the solvent in countercurrent contact with solution flowing from the column to deprive the vapors of their solvent content, and withdrawing the stripped solvent and returning the hydrocarbon vapors thus separated from the solvent to the original batch under its liquid surface, until the hydrocarbons other than butadiene are substantially eliminated from the batch.

5. The method of claim 4 in which the stripped solvent is cooled and recirculated through the column.

DAVID CRAIG. WALDO L. SEMON.

CERTIFICATE OF C ORREC'I'ION.

Patent No. 2,366,} 61.

January 2, 19145.

ALDO L. SEION; ET AL.

It is hereby certified that error appears in the printed specification of theebove numbered patent requiring correction as follows: Page 1, first column, lines 1 ,6 to 1+5 inclusive, for "drawing one e nbodicommunicates with a fractionating column 5 w cally" read --drawing one embodiment of the apparatus is shown diagrammatically; and that the saIdLetters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of May, A. D. 1915.

(Seal) Leslie Frazer Acting Commissioner of Patents. 

